1. Field of the Disclosure
The disclosure generally relates to photostabilized compositions containing an α-cyano-β,β-diphenylacrylate photostabilizer for a UV-absorbing naphthalate compound and, more specifically, to a naphthalate polymer composition containing an α-cyano-β,β diphenylacrylate photostabilizer. The disclosure further relates to polymer blends containing a naphthalate polymer and an α-cyano-β,β diphenylacrylate photostabilizer for the naphthalate polymer. The disclosure also is directed to methods of preparing and using photostabilized naphthalate or polyester-containing compositions.
2. Brief Description of Related Technology
Ultraviolet radiation from the sun or artificial sources can damage materials and/or coatings containing photoactive substances, such as photoactive polymers, pigments and dyes, by altering chemical bonds in the structure of the polymer, pigment, or dye. This photodegradation can lead to color fading, loss of gloss, and/or loss of physical and protective properties of a photodegradable or photoactive polymer or coating. Understandably, photostabilizing or photostabilization is the process or effect of preventing the photodegradation of photoactive substances. In particular, photostabilizing can be increasing the light fastness of a composition, preventing yellowing, or color formation, and delaying or preventing photochemical reactions that adversely affect photoactive substances.
One method to protect photoactive substances is through the use of UV filters; one class of materials particularly suited to act as a UV filters are naphthalate polyesters, for example those patented by this assignee. Naphthalate polyesters are suitable UV filters because they have very high extinction coefficients and subsequently low transmission of ultraviolet (UV) radiation. Additionally, the incorporation of naphthalates into polyester polymers increase the polymer's thermal and structural stability, decrease the polymer's gas permeability, and dramatically block the transmission of UV radiation through the polymer. The UV filtering and improved physical characteristics have led to the use of naphthalate polymers and blends in a wide range of applications including beverage and personal care product packaging, protective screening films, sail cloth fiber and as an additive stabilizer in sunscreens and cosmetics.
While efficiently absorbing UV radiation, naphthalates dissipate (emit) the absorbed energy through fluorescence. Fluorescence is a type of luminescence in which an atom or molecule emits radiation, i.e., a photon, in passing from a higher to a lower electron state, as described in my co-pending application Ser. No. 11/891,280 filed Aug. 9, 2007, herein incorporated by reference. The term is restricted to phenomena in which the time interval between absorption and emission energy is extremely short (10−12 to 10−6 second). This fluorescence can be a positive attribute in enabling the ready detection of naphthalate containing polymers or in the development of fluorescent coatings and inks. Alternatively, the high absorption of UV radiation can produce color formation or yellowing after exposure to UV light. Although this yellowing may not impact mechanical and physical properties of the polymer, it is generally undesirable. The fluorescence, color formation, or yellowing phenomena are of concern especially in packaging of products when the product's appearance is to be as close to its natural state as desired. For example, in the packaging of foods and beverages, if food or beverages were inside a poly(ethylene-2,6-naphthalene dicarboxylate) (“PEN”) container they may appear unnaturally colored.
Quenching fluorescence eliminates or reduces photon emission by providing an alternative pathway for the excited state energy, such as radiative loss (heat), or intersystem crossing to an excited triplet state. Methods to quench fluorescence in PEN have been disclosed, for example see references cited in U.S. Pat. No. 6,001,952. These examples disclose the use of o-chlorophenol to quench PEN fluorescence in chloroform solutions. Dissolving PEN in a chloroform solution to disperse a fluorescence quencher, however, is not practical since the PEN must have a low molecular weight to dissolve in the chloroform solution and only very dilute PEN solutions can be prepared.
Other compounds used to quench naphthalate fluorescence include: benzotriazoles, cyanoacrylates, benzophenones, and benzoxazinones (JP Pat. No. 08225672); cyclic imino esters or quinoxalines (EP Pat. No. 0711803); and benzylidene compounds (U.S. Pat. Nos. 4,617,374, 4,707,537, and 6,001,952). Many of these examples are disadvantageous because they require post production coating of fluorescent materials, show inadequate reduction in the fluorescence from fluorescent materials, or are only effective in very dilute solutions. Accordingly, there is a need for naphthalate compositions having a reduced fluorescence without deleteriously affecting the physical properties of the polymer.
Generally, the prior art does not teach or suggest to one of ordinary skill in the art how to quench the fluorescence of naphthalate compounds and compositions with α-cyano-β,β-diphenylacrylates.